Field of the Invention
This invention generally relates to check valves, and, in particular, to tide gate valves.
Description of Related Art
A check valve is essentially a valve which allows fluid flow in only one direction through a conduit, while closing and preventing back or reverse flow, when back pressure builds up downstream of the valve to a level greater than the upstream fluid pressure head.
One example where the fluid backflow problem is especially acute occurs where such valves are used to handle storm sewer effluent. Virtually all municipalities near waterways have storm sewer pipes which empty into the waterways. When there is a storm, storm water from the streets runs into these sewer pipes and flows 1 into the waterways. When the tide is in, or river level is high, these sewer pipes back fill with the water from the waterway. This leaves no, or reduced storage capacity in the sewer pipes. In the event there is a large cloudburst or storm during the time that the tide is in, all, or a portion of the storm water cannot get in the sewer because the sewer pipes are at least partially filled. This causes street flooding.
Further, sewage treatment plants are often located at sea level and/or the lowest point possible of a municipality. They discharge a large quantity of water after treatment of sewage. Where such treatment plants discharge into a body of salt water, positive shut off is mandatory to prevent salt water intrusion. Salt water intrusion is the backflowing of salt water into the plant. Salt water intrusion must be prevented because salt water will destroy the ongoing biological treatment of sewage, forcing the plant to discharge raw sewage into the waterways, which is a situation that must be avoided.
The cost to water treatment facilities to correct the problems created by a malfunctioning check valve can be enormous. Prior art metal check valves have a tendency to have higher head loss pressures and malfunction due to rust clogging hinges associated with such valves. Prior art rubber valves suffer from the higher head loss pressure limitations described above.
Another example where the fluid backflow problem is especially acute is where the check valves are used in chemical plants or municipal waste treatment plants. In such applications, it is desired to permit waste water or treatment chemicals to enter a reaction vessel or pond from a storage container without permitting the contents of the reaction vessel to backflow into a storage container as the chemical reactions proceed.
To address the previously described problems, various types of check valves have been developed. One type of check valve that has been developed to counter these problems is known as a tide gate type check valve. An example of a tide gate type check valve is described in U.S. Pat. No. 5,769,125. However, while the check valve described in U.S. Pat. No. 5,769,125 addresses the previously described backflow problems, the check valve requires a finite minimum amount of upstream pressure greater than the downstream pressure before the valve will open. For example, it may require 13 inches of positive differential pressure before a 12 inch diameter valve will open. At this pressure, the valve opens abruptly from fully closed to partially open, commonly referred to as snapping open. In many applications, this is undesirable.
Thus, it is desirable to provide an improved tide gate check valve that requires a lower amount of positive differential pressure to “snap” open. It is also desirable to provide a tide gate check valve that has a lower ratio of lateral stiffness to the longitudinal stiffness which in turn reduces the ratio of headloss (pressure drop in the forward flow direction) to backpressure capability (pressure withstanding capability in the reverse direction when the valve is closed).